Comment 5 for bug 1390004

in my environment, i found the root cause:
in mediastreamer2/src/audiofilter/alsa.c, linphone calls snd_pcm_hw_params_set_channels() with channel = 1. but my audio card driver does not support mono. i've tested with aplay a mono wave file and get no sound either.
how to set linphone to use stereo call?